Interconnect scaling

ABSTRACT

Methods of forming an interconnect structure include depositing a first conductive material on a substrate. Aspects include subtractively etching the conductive material to form a patterned first conductive layer, and depositing a dielectric layer on interconnect structure. Aspects also include depositing a second conductive material on the dielectric layer and removing the second conductive material through the top of the second metal liner.

DOMESTIC PRIORITY

This application is a Continuation of U.S. patent application Ser. No.15/166,570 filed May 27, 2016, entitled “INTERCONNECT SCALING,” which isa divisional of U.S. patent application Ser. No. 15/009,108 filed Jan.28, 2016, entitled “ INTERCONNECT SCALING” the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND

The present invention relates to methods for fabricating metal wiringlayers of a semiconductor device, and more specifically, to methods offabricating interconnect structures for semiconductor devices withminimized resistance and improved time dependent dielectric breakdown(TDDB) performance.

An integrated circuit (IC) device may be formed with millions oftransistors and other circuit elements that are fabricated on a singlesilicon crystal substrate (wafer). For the IC device to be functional,multi-level or multi-layered interconnection schemes such as, forexample, dual damascene wiring (interconnect structures) or wiringformed by subtractive etch, are fabricated using BEOL (back end of line)techniques to connect the circuit elements distributed on the surface ofthe device. BEOL technologies must be continuously optimized throughchanges in process flows and material used in order to build highperformance structures as critical dimensions decrease. For example,etching of small profiles using thin masking layers becomes increasinglyproblematic with regard to etch profile control (controlling shape ofhole or trench being formed) or control of etching damage and residues.Maximizing metal volume for a given space is difficult with currenttechnologies.

SUMMARY

According to one embodiment, a method of forming an interconnectstructure includes depositing a first conductive material on asubstrate. The method also includes subtractively etching the conductivematerial to form a patterned first conductive layer. The method alsoincludes depositing a dielectric layer on the interconnect structure.The method also includes depositing a second conductive material on thedielectric layer. The method also includes removing the secondconductive material through the top of the second metal liner.

In another embodiment, a method of forming an interconnect structureincludes depositing a first dielectric layer on a first insulator layer.The method also includes patterning a dielectric space pattern in thefirst dielectric layer. The method also includes patterning a first viahaving a via vertical wall in the first insulator layer. The method alsoincludes depositing a first conductive material on the structure thatfills the first via. The method also includes patterning a first trenchpattern in the first conductive material by subtractive etching. Themethod also includes depositing a second dielectric layer on thestructure. The method also includes depositing a second metal liner onthe structure. The method also includes depositing a second conductivematerial on the structure. The method also includes polishing thestructure by CMP to form a second level metal structure having a secondlevel vertical wall. In some embodiments, the second metal line isdefined by the previous dielectric space and first trench pattern. Themethod also includes depositing a second insulator layer on thestructure.

In yet another embodiment, an interconnect structure includes a firstinsulator layer. The interconnect structure also includes a firstdielectric layer on the first insulator layer. The interconnectstructure also includes a subtractive etch feature comprising a firstconductive material, the subtractive etch feature having a firstsubtractive etch vertical wall, a second subtractive etch vertical wall,and an angle between the first vertical wall and a horizontal plane thatis less than 90 degrees. The interconnect structure also includes adamascene feature comprising a second conductive material, the damascenefeature having a first damascene vertical wall, a second damascenevertical wall, and an angle between the first damascene vertical walland the horizontal plane that is greater than 90 degrees. In accordancewith the embodiment, the first subtractive etch vertical wall isparallel to the second damascene vertical wall.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A depicts a cross sectional side view of an exemplary device withidealized interconnect structures defining metal wiring.

FIG. 1B depicts a cross sectional side view of another exemplary devicewith idealized interconnect structures defining metal wiring.

FIG. 1C depicts a cross sectional side view of an exemplary device withinterconnect structures defining metal wiring.

FIG. 1D depicts a cross sectional side view of an exemplary device withinterconnect structures defining metal wiring.

FIG. 1E is a scanning electron micrograph of a damascene structureformed by a conventional damascene process.

FIG. 2 depicts a cross sectional side view of an exemplary interconnectstructure in accordance with an embodiment.

FIG. 3 depicts a cross sectional side view of another exemplaryinterconnect structure in accordance with an embodiment.

FIG. 4 is a flow diagram of a method of forming an interconnectstructure in accordance with an exemplary embodiment.

FIGS. 5A to 5E illustrate an exemplary fabrication process of forming aninterconnect structure according to an exemplary embodiment, in which:

FIG. 5A is a cross-sectional view illustrating an interconnect structureafter patterning a conductive material by subtractive etching inaccordance with an exemplary embodiment;

FIG. 5B is a cross-sectional view illustrating the interconnectstructure after depositing a dielectric layer in accordance with anexemplary embodiment;

FIG. 5C is a cross-sectional view illustrating the interconnectstructure after depositing a second metal liner and a second conductivematerial in accordance with an exemplary embodiment;

FIG. 5D is a cross-sectional view illustrating the structure afterpolishing to the top of the dielectric layer in accordance with anexemplary embodiment;

FIG. 5E is a cross-sectional view illustrating the structure afterpolishing to the first conductive material in accordance with anexemplary embodiment.

FIG. 6 a flow diagram of a method of forming an interconnect structurein accordance with another exemplary embodiment.

FIGS. 7A to 7J illustrate an exemplary fabrication process of forming aninterconnect structure according to an exemplary embodiment, in which:

FIG. 7A is a cross-sectional view illustrating an interconnect structureafter depositing a dielectric layer on an insulator layer in accordancewith an exemplary embodiment;

FIG. 7B is a cross-sectional view illustrating an interconnect structureafter patterning a dielectric space in the dielectric layer inaccordance with an exemplary embodiment;

FIG. 7C is a cross-sectional view illustrating an interconnect structureafter patterning a via in the dielectric layer and insulator layer inaccordance with an exemplary embodiment;

FIG. 7D is a cross-sectional view illustrating an interconnect structureafter depositing a metal liner and conductive material on the structurein accordance with an exemplary embodiment;

FIG. 7E is a cross-sectional view illustrating an interconnect structureafter conductive material is patterned to form metal structures and avia in accordance with an exemplary embodiment;

FIG. 7F is a cross-sectional view illustrating an interconnect structureafter depositing a second dielectric layer in accordance with anexemplary embodiment;

FIG. 7G is a cross-sectional view illustrating an interconnect structureafter patterning a second via pattern in accordance with an exemplaryembodiment;

FIG. 7H is a cross-sectional view illustrating an interconnect structureafter depositing metal liner and conductive material in accordance withan exemplary embodiment;

FIG. 7I is a cross-sectional view illustrating an interconnect structureafter polishing to the top of the second dielectric layer in accordancewith an exemplary embodiment;

FIG. 7J is a cross-sectional view illustrating an interconnect structureafter depositing a second insulator layer in accordance with anexemplary embodiment.

FIG. 8 is a cross-sectional view illustrating the structure of FIG. 7Hafter polishing to the top of the conductive material in accordance withan exemplary embodiment.

DETAILED DESCRIPTION

The invention relates to issues pertaining to interconnect scaling inBEOL techniques. It is desirable to increase the efficiency of metalplacement in wiring. Interconnect structures in BEOL technologies can beformed by damascene processes and etching. In some cases an opening inthe interconnect level may be a via, extending perpendicular to thesurface of IC completely through the interlayer dielectric (ILD) forconnecting an overlying wire of a higher wiring level or of the presentwiring level to an underlying wire of a lower wiring level. A filled viais typically simply referred to as a via or as a plug when connecting toan underlying first metallization (M1) or to an element of an underlyingMOS (metal oxide semiconductor) structure.

It is desirable to maximize the metal volume of metal wires for a givenspace between metal features. Conventional techniques, such asconventional damascene processes and subtractive etch processes, haveresulted in inefficient use of volume in interconnect structures becauseof the sidewall taper angle that results from such processing. Aconventional “damascene process,” forms conductors in-laid in thedielectric layer. In the context of integrated circuits, damascene meansformation of a patterned layer imbedded on and in another layer suchthat the top surfaces of the two layers are coplanar.

In an exemplary dual damascene process, a dielectric cap and insulatorlayer are deposited atop a preceding level having metal wiring. Theinsulator layer may have a dielectric constant k<3.0, such as SiCOH,SiON, TEOS, or silicon oxynitride. Photolithography can be used todefine a via and trench pattern to be transferred into the insulatorlayer and dielectric cap film. Reactive ion etch (RIE) can be used totransfer the photolithography pattern to the dielectric films. Trenchand via formation can involve multiple photolithography steps.Hydrofluoric acid can be used to clean the device and a metallizationprocess can be used to deposit a barrier metal, such as tantalum nitride(TaN/Ta), cobalt (Co) and ruthenium (Ru), and seed layer, such as copper(Cu), copper manganese (CuMn), copper aluminum (CuAl), and alloysthereof. Copper reflow or electroless plating with an over burden can beused to fill and planarize the interconnect structure. An anneal can beperformed to crystallize the metal. The structure can be polished bychemical mechanical polish to remove the metal overburden and repeatedas desired.

FIGS. 1A-1D illustrate the limitations in conventional damasceneprocesses. FIGS. 1A and 1B illustrate idealized metallization inexemplary interconnect structures. As is shown in FIGS. 1A and 1B, aconductive material 102, such as copper or another metal, can be formedin a dielectric layer 106 containing a low-k dielectric material byfilling in a trench that is patterned in the dielectric layer 106. A lowk dielectric material is a dielectric material with a dielectricconstant (k) less than 4. The dielectric layer 106 can be deposited ontop of an insulator layer 101 and be capped by a capping layer 100. Theconductive material 102 can be separated from the dielectric layer 106by a metal liner 104. In an ideal structure, the conductive material 102and metal liner 104 in the trenches are shaped with 90 degree angles,such that they form rectangular or square shapes when viewed in crosssection as shown in FIGS. 1A and 1B. The filled trenches are separatedfrom each other by a top separation distance 108 that, in an idealizedsituation, is predetermined based on patterning and equal to a bottomseparation distance 110 of the filled trenches.

In some cases, it is desirable to maximize metal volume to lower metalwire resistances. As shown in FIG. 1B, in an ideal situation the metalvolume can be increased by increasing the width of the trenches andfilling the trenches with a greater volume of conductive material. Inincreasing the metal width of the lines as shown in FIG. 1B the topseparation distance 108 becomes smaller. It is noted that for FIG. 1Aand FIG. 1B, the spacing is uniform from the top to the bottom of thefilled trench. This is idealized and not representative of truestructures formed by damascene processes because of the tendency togenerate tapered profiles. Furthermore, such structures with rectangularshapes are difficult to fill with metal.

FIGS. 1C and 1D illustrate approximate trench shapes that could beexpected after a conventional damascene process. As is shown in FIGS. 1Cand 1D, the metal liner 104 and conductive material 102 in the trenchesdoes not form 90 degree angles and the top separation distance 108 isnot uniform from the top of the trench to the bottom. Thus, if it isdesired to increase the volume of conductive material 102 from thatillustrated in FIG. 1C to that illustrated in FIG. 1D, top separationdistance 108 can become undesirably close and can compromise deviceperformance and reliability. FIG. 1E is a photograph depicting metalstructures formed by damascene techniques. It is known that minimumconductor-to-conductor (wire-to-wire or wire-to-via) spacing depends onthe taper angle of the conductive material 102 and metal liner 104,illustrated for example in FIGS. 1C-D, in the trenches. For example, itis known that electrical discharge and time dependent dielectricbreakdown (TDDB) are strongly dependent upon the separation distance 108at the top of the trenches.

Accordingly, embodiments of the invention provide BEOL interconnectstructures that enhance the efficiency of metal placement in wiring bymaximizing the metal volume for a given space between metal features.Moreover, embodiments of the invention can eliminate weak interfacesthat would be prone to fail by TDDB and can provide interconnectstructures that have enhanced reliability. In some embodiments, theinterconnect structures have a uniform or fixed metal spacing from thetop of the metal line to the bottom of the line between two adjacentmetal features. In some embodiments, the interconnect structures caneliminate critical interfaces between adjacent metal features.

FIG. 2 illustrates an exemplary interconnect structure according to anembodiment. The interconnect structure includes first conductivematerial 202 patterned on a substrate 200. The first conductive material202 forms a first conductive wire 201 that has a trapezoidal shape whenviewed in cross section with two first layer vertical walls 204 that aretapered. The first conductive material 202 can be patterned bysubtractive etching. The taper is such that the angle a between thevertical wall and the substrate is less than 90 degrees. Theinterconnect structure includes a dielectric layer 206 and preferably afirst metal liner 203 and 204. The interconnect structure includes asecond conductive material 208 separated from the dielectric layer 206by a second metal liner 210 and 211. The second conductive material 208can have the same composition as the first conductive material 202 orcan have a different composition. The second metal liner 210, 211 canhave the same composition as the first metal liner 203, 204 or can havea different composition. The second conductive material 208 can form asecond conductive wire 211 that has a trapezoidal shape when viewed incross section with two second layer vertical walls 209 that are tapered.The taper is such that the angle β is greater than 90 degrees and thesecond layer vertical walls 209 run parallel to the first layer verticalwalls 204. The second conductive wire 211 can be formed by a damasceneprocess.

Conductive material, including first conductive material 202 and secondconductive material 208, is a conductive material that is suitable forconductors, conductive vias, and conductive wire. Conductive material208 can be a conductive metal, such as tungsten (W), copper (Cu),aluminum (Al), silver (Ag), cobalt (Co), gold (Au), molybdenum (Mo), andalloys thereof. In some embodiments, first conductive material 202 andsecond conductive material 208 are the same material. In someembodiments, first conductive material 202 and second conductivematerial 208 are different materials.

The dielectric layers can include any suitable dielectric material usedin interconnect structures and can be the same or different. Thedielectric layer can be a single layer or, more preferably, is acomposite of several layers including adhesion layers or etch stoplayers. For example, the dielectric layer 206 can include a silicondioxide layer and a carbon containing silicon oxide layer; thedielectric layer 206 can include several layers having different carboncontents; the dielectric layer 206 can include a nitrogen containinglayer; the dielectric layer 206 can include a porous layer. In someembodiments, the dielectric layer has a dielectric constant less than orequal to four. In a preferred embodiment, the dielectric layer 206includes SiO₂ or carbon doped oxide (SiCOH). Preferably, the dielectriclayer 206 is deposited in a conformal fashion.

Deposition is any process that grows, coats, or otherwise transfers amaterial onto the wafer. Available technologies include, but are notlimited to, thermal oxidation, physical vapor deposition (PVD), chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE)and more recently, atomic layer deposition (ALD) among others.

Removal is any process that removes material from the wafer: examplesinclude etch processes (either wet or dry), and chemical-mechanicalplanarization (CMP), etc. In some embodiments, removal includes dryetch, such as reactive ion etching (RIE) or ion beam etch (IBE).

Patterning is the shaping or altering of deposited materials, andgenerally involves lithography. For example, in conventionallithography, the wafer is coated with a chemical called a photoresist;then, a machine called a stepper focuses, aligns, and moves a mask,exposing select portions of the wafer below to short wavelength light;the exposed regions are washed away by a developer solution. Afteretching or other processing, the remaining photoresist is removed.Patterning also includes electron-beam lithography, nanoimprintlithography, and reactive ion etching.

As used herein, the articles “a” and “an” preceding an element orcomponent are intended to be nonrestrictive regarding the number ofinstances (i.e. occurrences) of the element or component. Therefore, “a”or “an” should be read to include one or at least one, and the singularword form of the element or component also includes the plural unlessthe number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” arenon-limiting terms and not intended to refer to any single aspect of theparticular invention but encompass all possible aspects as described inthe specification and the claims.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

FIG. 3 illustrates another exemplary interconnect structure according toan embodiment. The interconnect structure includes a first layer 330including a first insulator layer 300 in contact with a first dielectriclayer 306. The first dielectric layer 306 can contain a plurality ofmetal features 312, 314, 315, 316, 320, 321 patterned in the firstdielectric layer with subtractive etch processes, damascene processes,or a both subtractive etch and damascene processes. Subtractive etchfeatures forming metal lines 315 and 314 form a trapezoidal shapewherein an angle alpha is formed between a vertical wall and thehorizontal plane and alpha is less than 90 degrees. A second dielectriclayer 318 can be deposited on top of first dielectric layer 306 and oneor more metal features that are formed by subtractive etch processes,314 and 215, in the first layer 330. Damascene features forming metallines 312 and 316 form a trapezoidal shapes wherein one or more anglesbeta are formed between a vertical wall and the horizontal plane andbeta is greater than 90 degrees. Some metal features are conductive vias320, 321 that extend from the one interconnect layer to anotherinterconnect layer (i.e., connecting metal lines from one level toanother). As shown in FIG. 3, vias 320, can extend from first dielectriclayer through the first insulator layer 300 to a layer beneath thestructure, and may underlie metal line features formed damasceneprocesses or features formed by multiple damascene processes 320. Alsoas shown in FIG. 3, vias 321, can extend from first dielectric layerthrough the first insulator layer 300 to a layer beneath the structure,and may underlie metal line features formed by subtractive etchprocesses 315.

The structure can include a second layer 340, which can include a secondinsulator 302 and a third dielectric layer 308 on top of the secondinsulator 302. The second layer 340 can include a plurality of metalfeatures, including subtractive etch features 314 and 315, damascenefeatures 312, 316, and conductive vias 320, 321 that extend from thesecond layer 340 to the first layer 330. A fourth dielectric layer 322can be deposited on top of the third dielectric layer 308 and one ormore metal features of the second layer 340. The device can also includea third insulator 304 covering the second layer 340. The metal featuresmay be lined with a metal liner 320.

Insulator layers 300, 302, 304 can form a dielectric barrier. In amulti-layered device, such as the device shown in FIG. 3, the insulatorlayers 300, 302, 304 the material used for each layer can be the same ordifferent. Dielectric materials that can be used for the substrate andinsulator layers include any now known or later developed dielectriclayer such a silicon carbide (SiC), silicon nitride (Si₃N₄), silicondioxide (SiO₂), and nitrogen or hydrogen doped silicon carbide(SiC(N,H)).

Any suitable liner material may be used for the metal liners 203, 210,and 320, and the material used for each of the liners 203, 210, and 320may be the same or different. Typical liner materials include tantalum(Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN),tungsten (W), ruthenium (Ru) and ruthenium nitride (RuN).

FIG. 4 is a flowchart of a method 400 of forming an interconnectstructure according to one exemplary embodiment. The method 400includes, as shown at block 402, patterning a first conductive materialon a substrate by subtractive etching and depositing a first metal lineron the patterned conductive material. Next, as shown at block 404, themethod 400 includes depositing a metal liner on the patterned conductivematerial and this can be done by utilizing a selective depositionprocess. The method also includes, as shown at block 406, depositing adielectric layer. The dielectric layer can be a conformal dielectriclayer. The method 400 then includes, as shown at block 410, depositing asecond metal liner on the underlying topography. Then, as shown at block412, the method 400 includes depositing a second conductive material onthe patterned dielectric layer. Depositing the second conductivematerial on the patterned dielectric layer can involve utilizing thetopography to form a second conductive material by a damascene process.As shown at block 414, the method then includes removing the secondconductive material to the top of the dielectric layer, for example bypolishing. In some embodiments, the second conductive material isremoved to the top of the dielectric layer by chemical mechanicalplanarization (CMP). Then, as shown at block 416, in some embodiments,the second conductive material is further removed to the top of thefirst conductive material.

FIGS. 5A-5E illustrate an exemplary method of forming an interconnectstructure according to an embodiment. FIG. 5A is a cross-sectional sideview illustrating an interconnect structure of an embodiment afterpatterning a first conductive material 202 on a substrate 200 bysubtractive etch and lining the patterned first conductive material witha first metal liner 203. In this example the first metal liner 203 isformed by a selective deposition process such as CVD or electrolessplating. FIG. 5B illustrates the structure after depositing a dielectriclayer 206 on the structure forming the trenches 500. FIG. 5C illustratesthe structure after depositing a second metal liner 210 and a secondconductive material 208, also referred to as an overburden, on thepatterned dielectric layer. FIG. 5D illustrates the structure after thestructure, including the overburden, is polished to the level of the topof the dielectric layer. As illustrated in FIG. 5E, the structure can,in some embodiments, optionally be further polished to the firstconductive material.

FIG. 6 is a flowchart of another exemplary method 600 of preparing aninterconnect structure according to an embodiment. The method 600includes, as shown at block 602, depositing a first dielectric layer ona first insulator layer. Next, as shown at block 604, the method 600includes patterning a dielectric space in the first dielectric layer.Then, as shown at block 606, the method 600 includes patterning a firstvia pattern in the first dielectric layer and the first insulator layer.Then, as shown at block 608, the method 600 includes depositing a metalliner and a conductive material on the structure. Then, as shown atblock 610, the conductive material is patterned, for example bysubtractive etch, to form metal structures and a first via. The method600 next includes, as shown at block 612, depositing a second dielectriclayer. The method 600 also includes, as shown at block 614, patterning asecond via pattern. In some embodiments, the second via pattern canextend through the first dielectric layer, second dielectric layer, andthe first insulator layer. Then, as shown at block 616, the method 600includes depositing a metal liner and conductive material on thestructure. Next, as shown at block 618, the structure is polished to adesired height. In some embodiments, the structure is polished to thetop of the second dielectric layer. In some embodiments, the structureis polished to the top of the first conductive material, as shown inblock 620. Then, as shown at block 622, a second insulator layer isdeposited on the device. In some embodiments, the method can be repeatedin whole or part to add further layers to the device.

FIGS. 7A-7J illustrate another exemplary method of forming aninterconnect structure according to an embodiment. FIG. 7A is across-sectional side view illustrating an interconnect structure of anembodiment after depositing a first dielectric layer 306 on a firstinsulator layer 300. FIG. 7B illustrates the structure after patterninga dielectric space 701 in the first dielectric layer 306. FIG. 7Cdepicts an interconnect structure after patterning a first via pattern700 in the first dielectric layer 306 and the first insulator layer 300.For example, the first via pattern 700 can be formed by a damasceneprocess.

FIG. 7D illustrates the structure after depositing a metal liner 320 anda conductive material 208 on the structure. FIG. 7E illustrates anexemplary structure after the conductive material 208 is patterned, forexample by subtractive etch, to form metal structures 702 and a firstvia 321. A metal liner 320 can be deposited on the metal structures by aselective deposition process, as illustrated. The metal liner 320 can bethe same material or a different material than that deposited on thedielectric layer. FIG. 7F illustrates the structure after depositing asecond dielectric layer 318 on the metal liner 320, first dielectriclayer 306, and metal structures 310, 702. FIG. 7G illustrates thestructure after patterning a second via pattern 704. In someembodiments, the second via pattern 704 can extend through the firstdielectric layer 306, second dielectric layer 318, and the firstinsulator layer 300. FIG. 7H illustrates the structure after depositinga metal liner 320 and conductive material 208 on the structure. FIG. 7Iillustrates the structure after the structure is polished, for exampleby CMP, to the top of the second dielectric layer 318. FIG. 7Jillustrates the structure after depositing a second insulator layer 302on the device.

FIG. 8 illustrates an exemplary structure after the structure that isfurther polished prior to adding a second insulator layer to the top ofthe first conductive material 320.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. An interconnect structure comprising: a firstlayer comprising: a first insulator layer; a first dielectric layer onthe first insulator layer; a subtractive etch feature comprising a firstconductive material, the subtractive etch feature having a firstsubtractive etch vertical wall, a second subtractive etch vertical wall,and an angle between the first subtractive etch vertical wall and ahorizontal plane that is less than 90 degrees; and a damascene featurecomprising a second conductive material, the damascene feature having afirst damascene vertical wall, a second damascene vertical wall, and anangle between the first damascene vertical wall and the horizontal planethat is greater than 90 degrees; wherein the first subtractive etchvertical wall is parallel to the second damascene vertical wall; and asecond layer comprising: a second insulator layer; and a metal feature;and a conductive via that extends from the second layer to the firstlayer.
 2. The interconnect structure according to claim 1, wherein themetal feature comprises a second subtractive etch feature, the secondsubtractive etch feature comprising a third conductive material, thesubtractive etch feature having a third subtractive etch vertical wall,a fourth subtractive etch vertical wall, and an angle between the thirdsubtractive etch vertical wall and the horizontal plane that is lessthan 90 degrees,
 3. The interconnect structure according to claim 2,wherein the conductive via that extends from the second layer to thefirst layer underlies the second subtractive etch feature.
 4. Theinterconnect structure according to claim 1, wherein the metal featurecomprises a second damascene feature, the second damascene featurecomprising a third damascene vertical wall, a fourth damascene verticalwall, and an angle between the third damascene vertical wall and thehorizontal plane that is greater than 90 degrees.
 5. The interconnectstructure according to claim 1, further comprising a third dielectriclayer on top of the second insulator layer.
 6. The interconnectstructure according to claim 5, further comprising a fourth dielectriclayer.
 7. The interconnect structure according to claim 1, furthercomprising a metal liner.
 8. The interconnect structure according toclaim 7, wherein the metal feature is lined with the metal liner.
 9. Theinterconnect structure according to claim 1, wherein the subtractiveetch feature is lined with the metal liner.
 10. The interconnectstructure according to claim 1, wherein the damascene structure is linedwith the metal liner.
 11. The interconnect structure according to claim1, wherein the first dielectric layer has a dielectric constant lessthan or equal to
 4. 12. The interconnect structure according to claim 1,wherein the first dielectric layer comprises silicon dioxide.
 13. Theinterconnect structure according to claim 1, wherein the firstdielectric layer comprises carbon doped oxide.
 14. The interconnectstructure according to claim 1, wherein the first dielectric layer is acomposite layer.
 15. The interconnect structure according to claim 14,wherein the first dielectric layer comprises an adhesion layer.
 16. Theinterconnect structure according to claim 14, wherein the firstdielectric layer comprises an etch stop layer.
 17. The interconnectstructure according to claim 14, wherein the first dielectric layercomprises nitrogen.
 18. The interconnect structure according to claim14, wherein the first dielectric layer comprises a porous layer.
 19. Theinterconnect structure of claim 1, further comprising a second via. 20.The interconnect structure of claim 19, wherein the second via extendsfrom the first dielectric layer through the first insulator layer to athird layer.